OLIGOSACCHARIDE SPECIFICITY OF NORMAL HUMAN HEPATOCYTE ALPHA-1-3 FUCOSYL-TRANSFERASE

A purified alpha1-3 fucosyltransferase (alpha1-3 FT) was recovered in the Golgi fraction of isolated hepatocytes from normal human liver tis sue. The efficiency of purification was controled by measurement of fu cose transfer to asialotransferrin (for alpha1-3 FT), to phenyl-beta-D -galactose (for alpha1-2 FT) and to 2' fucosyl lactose (for alpha1-3/4 FT). The initial hepatocyte isolation step got rid of 97% and 94% of alpha1-2 and alpha1-3/4 total liver FT, respectively. After Golgi enri chment (26-fold purification and a yield of 7.6%), alpha1-3 FT extract expressed a specific activity of 2 pM/min per mg protein. When incuba ted in optimized conditions with type 1, 2 or 6 oligosaccharide accept ors (10 mM), hepatocellular alpha-3 FT efficiently transferred fucose to N-acetyllactosamine and its 3' sialylated derivative, but poorly to lactose. When incubated with neutral or sialylated biantennary N-glyc ans, the enzyme expressed the highest affinity (K(m) = 0.38 mM) for th e 3' bisialylated derivative. This suggests that hepatocellular alpha1 -3 FT is involved in the synthesis of sialosyl Le(x) determinants on c irrhotic alpha1AGP.